Refrigerant evaporator

ABSTRACT

In a refrigerant evaporator, a core has tubes that are arranged in a core width direction and at least in two rows including a first row and a second row. The first row is disposed downstream of the second row with respect to a flow direction of an external fluid. The tubes of the first row provide a refrigerant upward path and a refrigerant downward path. The core has a thickness equal to or less than 50 mm with respect to the flow direction of the external fluid, and a width equal to or greater than 220 mm with respect to the core width direction. The upward path is further than the downward path with respect to a refrigerant inlet disposed at an end of a first header tank, and has a width equal to or less than 95 mm with respect to the core width direction.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2007-110889 filed on Apr. 19, 2007, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a refrigerant evaporator for evaporating a refrigerant of a refrigerant cycle apparatus.

BACKGROUND OF THE INVENTION

A refrigerant evaporator is, for example, described in Japanese Unexamined Patent Application Publication No. 2001-324290 (U.S. Pat. No. 6,339,937). In the described refrigerant evaporator, a core as a heat exchanging part includes a plurality of tubes extending in an up and down direction. The tubes are stacked in a horizontal direction (e.g., a core width direction) and arranged in two rows with respect to a flow direction of air. An upper tank is disposed at upper ends of the tubes of each row, and a lower tank is disposed at lower ends of the tubes of each row. Further, separators are provided in the upper tanks.

In the described refrigerant evaporator, a refrigerant inlet is disposed at an end of the upper tank that is in communication with the tubes in a downstream row (hereinafter, air-downstream row) with respect to the air flow, and a refrigerant outlet is disposed at an end of the other upper tank that is in communication with the tubes in an upstream row (hereinafter, air-upstream row) with respect to the air flow. The refrigerant inlet and the refrigerant outlet are disposed on the same side of the refrigerant evaporator with respect to the core width direction. Thus, a refrigerant flows through the tubes of the air-downstream row while making U-turn through the lower tank that is in communication with the tubes of the air-downstream row, and then flows through the tubes of the air-upstream row while making U-turn through the other lower tank that is in communication with the tubes of the air-upstream row. Namely, the evaporator is configured such that two U-turn paths of the refrigerant are provided. The refrigerant is discharged from the refrigerant outlet. The refrigerant is evaporated while flowing through the tubes by exchanging heat with the air flowing outside of the tubes.

SUMMARY OF THE INVENTION

In a refrigerant evaporator, it has been recently required to reduce a thickness of a core in order to reduce an installation space and a weight. However, in a refrigerant evaporator in which tubes are stacked in plural rows with respect to an air flow, in a case where a thickness of a core, that is, a dimension of the core with respect to an air flow direction is reduced, for example, to equal to or smaller than 50 mm, heat capacity is reduced. In a case where such a refrigerant evaporator is employed to a refrigerant cycle apparatus, liquid refrigerant is likely to stagnate in the core due to the lack of heat capacity when an operation of a refrigerant compressor of the refrigerant cycle apparatus is transferred from an ON state to an OFF state. Also, it is difficult to clear the stagnation of the liquid refrigerant even after the refrigerant compressor switched to the ON state.

The present invention is made in view of the foregoing matter, and it is an object of the present invention to provide a refrigerant evaporator, capable of reducing stagnation of liquid refrigerant therein.

According to an aspect of the present invention, a refrigerant evaporator includes a core, a first header tank, a second header tank, a refrigerant inlet, a refrigerant outlet. The core includes a plurality of tubes. The tubes are arranged in a core width direction and at least in two rows including a first row and a second row, the first row being located downstream of the second row with respect to a flow direction of an external fluid. The first header tank includes a first upper tank portion and a first lower tank portion. The first upper tank portion is in communication with upper ends of the tubes of the first row, and the first lower tank portion is in communication with lower ends of the tubes of the first row. The second header tank includes a second upper tank portion and a second lower tank portion. The second upper tank portion is in communication with upper ends of the tubes of the second row, and the second lower tank portion is in communication with lower ends of the tubes of the second row. The refrigerant inlet is disposed at an end of the first header tank. The refrigerant outlet disposed at an end of the second header tank. The end of the second header tank and the end of the first header tank are on the same side with respect to the core width direction. A first separation member is disposed in the first header tank such that a first upward path through which the refrigerant flows in an upward direction and a first downward path through which the refrigerant flows in a downward direction are provided by the tubes of the first row. The first upward path and the first downward path are adjacent to each other with respect to the core width direction. A second separation member is disposed in the second header tank such that a second upward path through which the refrigerant flows in the upward direction and a second downward path through which the refrigerant flows in the downward direction are provided by the tubes of the second row. The second upward path and the second downward path are adjacent to each other with respect to the core width direction. The core has a thickness equal to or less than 50 mm with respect to the flow direction of the external fluid. The core has a width equal to or greater than 220 mm with respect to the core width direction. The first upward path is located further than the first downward path with respect to the refrigerant inlet, and a width of the first upward path with respect to the core width direction is equal to or less than 95 mm.

In the above construction, since the width of the core is equal to or greater than 220 mm, an increase in pressure loss is slight and a decrease in heat exchange efficiency is suppressed. Although heat capacity is reduced due to the reduction of the thickness of the core, since the core has the width equal to or greater than 220 mm and the first upward path, which is the furthest from the refrigerant inlet in the paths provided by the tubes of the first row, has the width equal to or less than 95 mm, stagnation of the liquid refrigerant around a lower portion of the first upward path is easily cleared.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a perspective view of a refrigerant evaporator according to an embodiment of the present invention;

FIG. 2 is an enlarged view of a part of a core of the refrigerant evaporator according to the embodiment;

FIG. 3 is a schematic view for showing a general flow of a refrigerant inside of the refrigerant evaporator according to the embodiment;

FIG. 4 is a schematic view of an evaporator as a comparative example for showing a change of surface temperature of tubes in an air-downstream row as a time elapses since a refrigerant compressor is switched to an OFF state;

FIG. 5 is a schematic view of the evaporator as the comparative example for showing a change of surface temperature of the tubes in the air-downstream row as a time elapses since the compressor is switched to an ON state;

FIG. 6 is a graph showing a relationship between a width of a third path of an air-downstream row and efficiency of heat exchange of the evaporator according to the embodiment of the present invention;

FIG. 7 is a graph showing a relationship between a fin height and efficiency of heat exchange of the evaporator according to the embodiment of the present invention;

FIG. 8 is a graph showing a relationship between a core thickness and an increase in temperature of the evaporators during a transitional period of ON and OFF states of a refrigerant compressor based on a fin thermister;

FIG. 9 is a graph showing a relationship between a core thickness and an increase in temperature of the evaporators during the transitional period of the ON and OFF states of the refrigerant compressor based on an air thermister;

FIG. 10 is a chart showing a sensory evaluation relative to a variation in temperature of air at an air outlet and a variation in temperature of air downstream of an evaporator;

FIG. 11 is a schematic view of an evaporator and a general flow of a refrigerant therein according to another embodiment of the present invention;

FIG. 12 is a schematic view of an evaporator and a general flow of a refrigerant therein according to further another embodiment of the present invention; and

FIG. 13 is a schematic view of an evaporator and a general flow of a refrigerant therein according to still another embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT

Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings.

FIGS. 1 to 3 show an embodiment of the present invention. In the present embodiment, a refrigerant evaporator 1 (hereinafter, simply referred to as the evaporator 1) is, for example, employed to a refrigerant cycle apparatus for a vehicular air conditioner. In the refrigerant cycle apparatus, a refrigerant is compressed into a high temperature, high pressure refrigerant by a refrigerant compressor. The high temperature, high pressure refrigerant is cooled through a radiator, and is decompressed into a low temperature, low pressure refrigerant by a decompressing device. The low temperature, low pressure refrigerant is evaporated in the evaporator 1. In the present embodiment, the refrigerant is, for example, R134a. The radiator serves as a condenser for condensing the refrigerant discharged from the refrigerant compressor.

The evaporator 1 generally includes a core 2 as a heat exchanging part, an upper header tank 3, a lower header tank 4, and the like. The core 2 includes a plurality of tubes 20, a plurality of outer fins 26 and side plates 28. The tubes 20 and the outer fins 26 are alternately staked in a substantially horizontal direction. The side plates 28 are disposed along the outer fins 26 that are stacked in outermost layers. The outer fins 26 serve as heat exchanging fins. Hereinafter, a direction in which the tubes 20 and the outer fins 26 are stacked is referred to as a stacking direction. Also, a width W of the core 2 is measured in the stacking direction. Thus, the stacking direction is also referred to as a core width direction.

The tubes 20 are generally flat pipe members. For example, the tubes 20 are made by bending thin aluminum belt-like plate members. Although not illustrated, inner fins are provided inside of the tubes 20, and are joined to inner surfaces of the tubes 20.

In the core 2, the tubes 20 extend in an up and down direction. The tubes 20 are arranged in two rows, such as a first tube row 21 (e.g., air-downstream row) and a second tube row 22 (e.g., air-upstream row), with respect to a flow of air as an external fluid. The first tube row is disposed downstream of the second tube row 22 with respect to the air flow. In other words, the core 2 is disposed such that the first tube row 21 and the second tube row 22 are overlapped with each other with respect to an air flow direction. Hereinafter, the tubes 20 in the first tube row 21 are also referred to as tubes 20A, and the tubes 20 in the second tube row 22 are also referred to as tubes 20B.

The outer fins 26 are, for example, corrugate fins that are made by shaping thin aluminum belt-like plate members into a corrugate shape. The outer fins 26 are formed with louvers on the surfaces for increasing efficiency of heat exchange. The outer fins 26 are brazed with outer surfaces of the tubs 20.

The side plates 28 serve as reinforcement members of the core 2. The side plates 28 are, for example, formed by pressing aluminum flat plate members. Ends of each side plate 28 with respect to a longitudinal direction are flat, and a main portion of each side plate 28 other than the ends has a substantially U-shape in a cross-section defined perpendicular to a longitudinal direction of the side plate 28. The side plate 28 is brazed to the outer fin 26 such that an opening of the U-shape faces outside of the core 2 with respect to the stacking direction.

The upper header tank 3 generally includes a tank header, a plate header and a cap. The tank header and the plate header are joined to each other with respect to a longitudinal direction of the tubes 20. The plate header is disposed adjacent to the tubes 20, and the tank header is disposed opposite to the tubes 20 with respect to the plate header.

Each of the tank header and the plate header is formed into a predetermined shape from an aluminum plate member such as by pressing, for example. The tank header has two continuous semicircular shape or two continuous U-shape in a cross-section defined perpendicular to its longitudinal direction. Also, the plate header has two continuous semi-circular shape or two continuous U-shape in a cross-section defined perpendicular to its longitudinal direction. The tank header and the plate header are engaged and joined to each other such that a first upper-tank inner space and a second upper-tank inner space are provided between them. The first upper-tank inner space is provided downstream of the second upper-tank inner space with respect to the air flow direction.

The cap is disposed to cover an open end of a generally tubular body constructed of the tank header and the plate header. The cap is, for example, made by shaping an aluminum flat plate member such as by pressing. The cap is brazed with the end of the tubular body with respect to a longitudinal direction of the tubular body.

Further, the upper header tank 3 is provided with two separators 33, 34. The separator 33 is disposed in the first upper-tank inner space such that the first upper-tank inner space is separated into two chambers with respect to the longitudinal direction of the upper header tank 3, such as in a right and left direction of FIG. 3. The separator 34 is disposed in the second upper-tank inner space such that the second upper-tank inner space is separated into two chambers with respect to the longitudinal direction of the upper header tank 3, such as in the right and left direction of FIG. 3. The separators 33, 34 are brazed inside of the upper header tank 3. One of the chambers of the first upper-tank inner space (e.g., first upper chamber), which is located on a right side of the separator 33 in FIG. 3, is in communication with one of the chambers of the second upper-tank inner space (e.g., second upper chamber), which is located on a right side of the separator 34 in FIG. 3, through first communication holes 36.

The lower header tank 4 has a generally similar shape as the upper header tank 3. The lower header tank 4 includes a tank header, a plate header and caps. The tank header and the plate header form a generally tubular body. The caps are disposed at open ends of the tubular body with respect to a longitudinal direction of the lower header tank 4.

The lower header tank 4 forms a first lower-tank inner space and a second lower-tank inner space with respect to the air flow direction. The first lower-tank inner space is provided downstream of the second lower-tank inner space with respect to the air flow direction. Separators 43, 44 are brazed inside of the lower header tank 4. The separator 43 is provided in the first lower-tank inner space such that the first lower-tank inner space is separated into two chambers with respect to the longitudinal direction of the lower header tank 4. The separator 44 is provided in the second lower-tank inner space such that the second lower-tank inner space is separated into two chambers with respect to the longitudinal direction of the lower header tank 4. One of the chambers of the first lower-tank inner space, which is located on the right side of the separator 43 in FIG. 3, is in communication with one of the chambers of the second lower-tank inner space, which is located on the right side of the separator 44 in FIG. 3, through second communication holes 46.

Each of the upper and lower header tanks 3, 4 has insertion openings on a wall that faces the core 2. Ends of the tubes 20 and the ends of the side plates 28 are inserted to the insertion openings and brazed with the upper and lower header tanks 3, 4. Thus, the tubes 20 are in communication with the upper and lower header tanks 3, 4, and the ends of the side plates 28 are supported by the upper and lower header tanks 3, 4.

The upper header tank 3 includes a first upper tank 31 and a second upper tank 32. The first upper tank 31 is disposed downstream of the second upper tank 32 with respect to the air flow direction. The first upper tank 31 provides the first upper-tank inner space therein, and the second upper tank 32 provides the second upper-tank inner space therein.

The lower header tank 4 provides a first lower tank 41 and a second lower tank 42. The first lower tank 41 is disposed downstream of the second lower tank 42 with respect to the air flow direction. The first lower tank 41 provides the first lower-tank inner space therein, and the second lower tank 42 provides the second lower-tank inner space therein.

The upper ends of the tubes 20A of the first tube row 21 are connected to the first upper tank 31. The lower ends of the tubes 20A of the first tube row 21 are connected to the first lower tank 41. The first upper tank 31 and the first lower tank 41 constitute a first header tank 11 for distributing and collecting the refrigerant into and from the tubes 20A of the first tube row 21.

The upper ends of the tubes 20B of the second tube row 22 are connected to the second upper tank 32. The lower ends of the tubes 20B of the second tube row 22 are connected to the second lower tank 42. The second upper tank 32 and the second lower tank 42 constitute a second header tank 12 for distributing and collecting the refrigerant into and from the tubes 20B of the second tube row 22.

A connector 5 is brazed with an end of the upper header tank 3, such as a left end in FIG. 3. The connector 5 has a refrigerant inlet 51 as a refrigerant introducing portion for introducing the refrigerant into the evaporator 1 and a refrigerant outlet 52 as a refrigerant discharging portion for discharging the refrigerant from the evaporator 1. The refrigerant inlet 51 is in communication with an end (e.g., left end in FIG. 3) of the first lower tank 41 through a side passage 210. The refrigerant outlet 52 is in communication with an end (e.g., left end in FIG. 3) of the second upper tank 32.

That is, the first header tank 11 is provided with the refrigerant inlet 51 for introducing the refrigerant into the evaporator 1, and the second header tank 12 is provided with the refrigerant outlet 52 for discharging the refrigerant from the evaporator 1. Further, the refrigerant inlet 51 and the refrigerant outlet 52 are disposed on the ends of the first and second header tanks 11, 12, the ends being on the same side of the evaporator 1 with respect to the stacking direction, that is, the core width direction.

In the present embodiment, the refrigerant flows in the chamber of the first lower tank 41 from the refrigerant inlet 51 through the side passage 210, the chamber being on the left side of the separator 43 in FIG. 3. The refrigerant flows through the tubes 20A of the first tube row 21 in a generally S-shape or meandering manner while changing directions in the up and down direction. Further, the refrigerant is introduced into the tubes 20B of the second tube row 21 through the right chambers of the upper header tank 3. The refrigerant flows through the tubes 20B of the second tube row 22 in a generally S-shape or meandering manner while changing directions in the up and down direction. Then, the refrigerant is discharged from the refrigerant outlet 52. While flowing in the evaporator 1 in the above manner, the refrigerant is evaporated and thus the air is cooled by latent heat of evaporation.

The flow of the refrigerant in the evaporator 1 is described more in detail with reference to FIG. 3. The first tube row 21 is separated into three refrigerant paths by means of the separators 33, 43. Also, the second tube row 22 is separated into three refrigerant paths by means of the separators 34, 44.

As shown in FIG. 3, the refrigerant, which has been introduced in the first lower tank 41 through the side passage 210, passes through a first path 211 of the first tube row 21 in an upward direction as shown by an arrow P1. The refrigerant turns through the first upper tank 31 and flows into a second path 212 of the first tube row 21 in a downward direction as shown by an arrow P2. A part of the refrigerant, which has passed through the second path 212, turns through the first lower tank 41 and flows into a third path 213 of the first tube row 21 in the upward direction as shown by an arrow P3. The remaining refrigerant, which has passed through the second path 212, is introduced into the second lower tank 42 from the first lower tank 41 through the second communication holes 46 as shown by an arrow P4, and flows into a first path 221 of the second tube row 22 in the upward direction as shown by an arrow P5.

The refrigerant, which has passed through the third path 213 of the first tube row 21 in the upward direction, is introduced into the second upper tank 32 from the first upper tank 31 through the first communication holes 36 as shown by an arrow P6, and is merged with the refrigerant that has passed through the first path 221 of the second tube row 22 in the upward direction. As such, the third path 213 of the first tube row 21 and the first path 221 of the second tube row 22 are configured such that the refrigerant flows therein in parallel with each other.

The refrigerant, which has merged in the second upper tank 32, flows into a second path 222 of the second tube row 22 in the downward direction as shown by an arrow P7. Further, the refrigerant turns through the second lower tank 42 and flows into a third path 223 of the second tube row 22 in the upward direction as shown by an arrow P8. Thereafter, the refrigerant is discharged from the second upper tank 32.

As described in the above, the separators 33, 43 are respectively disposed in the first upper and lower tanks 31, 41 such that the first path 211 of the first tube row 21 provides a refrigerant upward current, the second path 212, which is adjacent to the first path 211, provides a refrigerant downward current, and the third path 213, which is adjacent to the second path 212, provides a refrigerant upward current. The separators 33, 43 serve as a first separation member.

On the other hand, the separators 34, 44 are respectively disposed in the second upper and lower tanks 32, 42 such that the first path 221 of the second tube row 22 provides a refrigerant upward current, the second path 222, which is adjacent to the first path 221, provides a refrigerant downward current, and the third path 223, which is adjacent to the second path 222, provides a refrigerant upward current. The separators 34, 44 serve as a second separation member.

The third path 213 is in communication with the right chamber (e.g., first upper chamber) of the first upper tank 31, and the first path 221 is in communication with the right chamber (e.g., second upper chamber) of the second upper tank 32. The first communication holes 36 are disposed at a connecting portion between the right chamber of the first upper tank 31 and the right chamber of the second upper tank 32, as first communication portions. The third path 213 is in communication with the right chamber of the first lower tank 41, and the first path 221 of the second lower tank 42 is in communication with the right chamber of the second lower tank 42. The second communication holes 46 are disposed at a connecting portion between the right chamber of the first lower tank 41 and the right chamber of the second lower tank 42, as second communication portions.

In the present embodiment, a thickness D of the core 2 with respect to the air flow direction is equal to or less than 50 mm, and a width W of the core 2 with respect to the stacking direction, that is, in the longitudinal direction of the header tanks 3, 4, is equal to or greater than 220 mm. For example, the thickness D is 38 mm. Further, the third path 213 of the first tube row 21, which is the furthest path in the first tube row 21 from the refrigerant inlet 51, is configured such that the refrigerant flows in the upward direction. In addition, a width L1 of the third path 213 with respect to the stacking direction is equal to or less than 95 mm. The third path 213 of the first tube row 21 serves as a first furthest section in the core 2.

Also, the first path 221 of the second tube row 22, which is the furthest path in the second tube row 22 from the refrigerant outlet 52, is configured such that the refrigerant flows in the upward direction. In addition, a width L2 of the first path 221 with respect to the stacking direction is equal to the width L1 of the third path 213. The first path 221 of the second tube row 22 serves as a second furthest section in the core 2.

In the above structure, since the third path 213 provides the upward refrigerant current and the width L1 of the third path 213 is equal to or less than 95 mm, stagnation of the refrigerant in the core 2 is reduced.

In an evaporator in which a refrigerant inlet and a refrigerant outlet are located at the same side with respect to a stacking direction of tubes, a refrigerant is likely to be excessively heated (super heated) in a third path of a second tube row, which is close to the refrigerant outlet. On the other hand, a liquid refrigerant is likely to be easily stagnated in a lower portion of a third path of the first tube row, which is the furthest portion in the core from the refrigerant inlet and outlet and where the air which has been cooled through the second tube row passes.

An evaporator having a conventional refrigerant flow pattern as a comparative example is employed to a refrigerant cycle apparatus, and a change of surface temperature of tubes in a first tube row (air-downstream row) when an operation of a refrigerant compressor is switched is examined. FIG. 4 shows the change of surface temperature as a time elapses since the refrigerant compressor is switched to OFF. FIG. 5 shows the change of temperature as a time elapses since the refrigerant compressor is switched to ON.

As shown in FIG. 4, after the compressor is switched to OFF, the surface temperature of the tubes in the air-downstream row gradually increases. However, a low temperature area remains in a lower portion of a second path, which is the furthest section in a core. That is, it is realized that stagnation of the liquid refrigerant occurs in the low temperature area.

As shown in FIG. 5, after the compressor is switched to ON and a refrigerant supply begun, the refrigerant is supplied into a near portion of the core 2 while urging the stagnated liquid refrigerant toward a further end with respect to the longitudinal direction of the header tank.

In an initial stage of the refrigerant supply, the refrigerant is mainly in a gas phase and the specific gravity of the gas refrigerant is small. Therefore, it is difficult to introduce the refrigerant into the tubes while entirely sweeping the liquid refrigerant. In a case where the thickness of the core is reduced, for example, equal to or less than 50 mm, the liquid refrigerant is likely to stagnate in the furthest path of the core from the refrigerant inlet due to the lack of heat capacity when the refrigerant compressor is switched to OFF. Further, it is difficult to clear the stagnated liquid refrigerant even after the refrigerant compressor is restarted. Also, the stagnation of the liquid refrigerant causes an increase in temperature during the transitional period of the ON and OFF of the refrigerant compressor.

As show in FIG. 5, it is realized that the gas refrigerant smoothly flows in a region within a width of 95 mm in the furthest path while urging the liquid refrigerant upward immediately after the refrigerant supply begun.

In the present embodiment, since the width W of the core 2 is equal to or greater than 220 mm, an increase in pressure loss is slight and a decrease in efficiency of heat exchange is easily suppressed. Although heat capacity is reduced due to the decrease in the thickness D of the core 2, such as equal to or smaller than 50 mm, since the width W of the core 2 is equal to or greater than 220 mm and the width L1 of the third path 213 of the first tube row 21 is equal to or less than 95 mm, the liquid refrigerant, which is stagnated in the lower portion of the third path 213, is smoothly introduced upward when the refrigerant supply is restarted. As such, the stagnation of the refrigerant is easily solved.

In general, in a cooling cycle apparatus of a vehicle air conditioner, a thermister is used as a temperature detecting device in order to reduce frost of the evaporator due to excess decrease in the temperature of the evaporator. For example, refrigerant supply is controlled in a manner that when the temperature of the evaporator detected by the thermister is excessively decreased, the refrigerant supply is stopped, and when the temperature of the evaporator increases to a predetermined level, the refrigerant supply is restarted. As examples of the thermister, a fin thermister and an air thermister are generally used. The fin thermister is interposed between the fins to directly contact the fin or tube and detects the temperature in a direct manner. The air thermister is disposed to detect the temperature of air after heat exchange in the evaporator.

In a case where the liquid refrigerant is stagnated in the core due to repetition of the ON and OFF of the compressor, it is difficult to clear the stagnation of the liquid refrigerant even when the refrigerant supply is stopped. In such a case, a region of the core where the refrigerant is not stagnated is increased in the temperature due to the air although the detected temperature of the fin thermister will not increase. As a result, the temperature of the core is likely to be increased entirely. In a case where the air thermister is used, if frost is generated and is grown due to evaporation of the stagnated liquid refrigerant, a region in which air is difficult to pass is increased in the core. Therefore, it is difficult to detect the temperature of the core. As a result, it is difficult to detect the frost.

On the other hand, in the core 2 of the present embodiment, since the stagnation of the liquid refrigerant is easily cleared, temperature distribution (transitional temperature difference) during the transitional period between ON and OFF of the refrigerant compressor is reduced. Thus, when the evaporator 1 of the present embodiment is employed to a vehicular air conditioner, air conditioning comfort of a passenger improves. Also, the frost of the evaporator 1 is reduced, and hence a cooling operation improves.

In an evaporator in which a thickness of a core with respect to the air flow direction is equal to or less than 50 mm, pressure loss is likely to be relatively increased. On the other hand, in the present embodiment, the chamber of the first upper tank 31, which is in communication with the third path 213 of the first tube row 21, is in communication with the chamber of the second upper tank 32, which is in communication with the first path 221 of the second tube row 22, through the first communication holes 36. Also, the chamber of the first lower tank 41, which is in communication with the third path 213 of the first tube row 21, is in communication with the first path 221 of the second tube row 22, through the second communication holes 46. As such, the refrigerant flows through the third path 213 of the first tube row 21 and the first path 221 of the second tube row 22 in the upward direction and in parallel with each other. Therefore, even when the thickness D of the core 2 is equal to or less than 50 mm, pressure loss of the refrigerant is reduced.

In a case where the core 2 has only two rows of the tubes, the width W of the core 2 can be at least 220 mm and at most 350 mm (220 mm≦W≦350 mm), and the width L1 of the third path 213 can be at least 50 mm and at most 95 mm (50 mm≦L1≦95 mm).

As shown in FIG. 6, when the width L1 is in a range between 50 mm and 110 mm, heat exchanging performance is maintained equal to or more than 95% relative to the maximum performance. Thus, by setting the width L1 in the range between 50 mm and 95 mm in the evaporator in which the width W of the core 2 is in the range between 220 mm and 350 mm, the stagnation of the refrigerant is reduced and the heat exchanging performance is improved.

With regard to the size of the communication holes 36, 46, each of the communication holes 36, 46 has an equivalent diameter d that is at least 0.55 mm and at most 3 mm (0.55 mm≦d≦3 mm). In the case where the equivalent diameter d of each communication hole 36, 46 is equal to or greater than 0.55 mm, clogging is reduced. In the case where the equivalent diameter d of each communication hole 36, 46 is equal to or less than 3 mm, resistance to pressure is sufficiently maintained.

In a case where a total opening area (e.g., total cross-sectional area) of the first communication holes 36 is greater than a total opening area (e.g., total cross-sectional area) of the second communication holes 46, the refrigerant is more introduced to the third path 213 of the first tube row 21 than to the first path 221 of the second tube row 22. In this case, therefore, temperature distribution is improved.

In a case where the total opening area of the first communication holes 36 is smaller than a total opening area of the second communication holes 46, the refrigerant is more introduced to the first path 221 of the second tube row 22 than to the third path 213 of the first tube row 21. In this case, therefore, the efficiency of heat exchange improves.

In the above example, the width L1 of the third path 213 of the first tube row 21 is equal to the width L2 of the first path 221 of the second tube row 22. Alternatively, the width L1 of the third path 213 can be smaller than the width L2 of the first path 221 (L1≦L2). In this case, since the amount of refrigerant passing through the first path 221 of the second tube row 22 is greater than the amount of refrigerant passing through the third path 213 of the first tube row 21. Because the degree of heat exchange in the second tube row 22 is larger than that of the first tube row 21, the efficiency of heat exchange is improved.

As another example, the width L1 of the third path 213 can be larger than the width L2 of the first path 221 (L1≧L2). In this case, areas where the temperature distribution is deteriorated are complemented between the first tube row 21 and the second tube row 22. In general, the liquid refrigerant is more distributed to a further position than a near position due to the inertial force when being introduced into tubes in the upward direction from a chamber of a lower tank. For example, when the refrigerant is introduced into the third path 213 of the first tube row 21, the liquid refrigerant is more introduced to the further tubes 20A, which are further from the second path 222, than to the near tubes 20A, which are near to the second path 222. Also, the liquid refrigerant easily drops to a near position due to the gravity when being introduced into tubes in the downward direction from a chamber of an upper tank. For example, when the liquid refrigerant is introduced into the second path 222 from the first path 221, the liquid refrigerant is more introduced to the near tubes 20B, which are near to the first path 221, than to the further tubes 20B, which are further from the first path 221. As such, in the case where the width L2 is smaller than the width L1, a portion of the third path 213 where the liquid refrigerant is less introduced is overlapped with a portion of the second path 222 where the liquid refrigerant is more introduced. As such, uneven distribution of the liquid refrigerant is complemented between the first tube row 21 and the second tube row 22.

In the present embodiment, the second tube row 22 provides the three refrigerant paths 221, 222, 223. The first and third paths 221, 223 provide the refrigerant upward currents and the second path 222 provides the refrigerant downward current.

In an evaporator, an effect of the pressure loss of the refrigerant is increased as a distance from a refrigerant outlet is reduced. Therefore, it is preferable that the refrigerant that has finished the heat exchange exists close to the refrigerant outlet 52 in view of the performance. Since the refrigerant outlet 52 is located at the end of the second upper tank 32, the third path 223 of the second tube row 22, which is the last path, is configured to provide the refrigerant upward current. Since the first path 221, which is the furthest path from the refrigerant outlet 52, also provides the refrigerant upward current, the second path 222 between the first path 221 and the third path 223 is configured to provide the refrigerant downward current. Accordingly, the second tube row 22 is configured to have the three paths 221, 222, 223.

For example, the width L1 of the third path 213 of the first tube row 21 and the width L2 of the first path 221 of the second tube row 22 are set such that the sum of the widths L1 and L2 and the width W of the core 2 satisfy a relationship of 0.24×W≦L1+L2≦0.36 W.

Under a representative condition in summer, the quality of vapor (dryness) of the refrigerant flowing into the third path 213 of the first tube row 21 and the first path 221 of the second tube row 22 is approximately 0.6, and the specific volume of the refrigerant is approximately 0.043. Further, the quality of vapor of the refrigerant flowing out of the third path 213 of the first tube row 21 and the first path 221 of the second tube row 22 is approximately 0.75, and the specific volume of the refrigerant is approximately 0.055. On the other hand, the specific volume of the refrigerant at the refrigerant outlet 52 is approximately 0.080.

As such, the average of the specific volume in the third path 213 of the first tube row 21 and the first path 221 of the second tube row 22 is 0.049, and the average of the specific volume in the second path 222 and the third path 223 of the second tube row 22 is 0.0675. The second and third paths 222, 223 provide two refrigerant paths and has the relationship of 0.049:0.0675×2=1:2.76 with respect to the core width direction. Based on this relationship, the sum of the width L1 and the width L2 and the width W of the core 2 satisfy a relationship of L1+L2=(1/2.76)×W≈0.36×W.

Under the representative condition in winter, the average of the specific volume in the third path 213 of the first tube row 21 and the first path 221 of the second tube row 22 is 0.03. The average of the specific volume in the second and third paths 222, 223 of the second tube row 22 is 0.0625. As such, the sum of the width L1 and the width L2 and the width W satisfy a relationship of L1+L2=(1/4.17)×W≈0.24×W.

Accordingly, the sum of the width L1 and the width L2 can be set to satisfy a relationship of 0.24×W≦L1+L2≦0.36×W, relative to the width W of the core 2.

For example, a dimension FH (FIG. 2) of the outer fin 26 with respect to the core width direction is at least 3 mm and at most 7 mm (3 mm≦FH≦7 mm), and a dimension TH (FIG. 2) of the tube 20 with respect to the core width direction is at least 1.1 mm and at most 2.3 mm (1.1 mm≦TH≦2.3 mm). Hereinafter, the dimension FH is referred to as the fin height FH, and the dimension TH is referred to as the tube height TH.

FIG. 7 shows the performance when the fin height FH and the tube height TH are varied in the core 2 having the thickness of 38 mm. In FIG. 7, the performance of a first example core having the thickness of 58 mm, which is an ordinary thickness, is defined as a reference performance. In a second example core in which only the thickness of the core is modified to 38 mm relative to the first example core, 92% of the reference performance is provided.

As shown in FIG. 7, when the fin height FH is in the range between 3 mm and 7 mm and the tube height TH is in the range between 1.1 mm and 2.3 mm, the performance of the core 2 exceeds the performance of the second example core. In FIG. 7, FP represents a pitch of the outer fins 26, TWT represents a wall thickness of the tube 20, and IFT represents a wall thickness of the inner fin.

FIGS. 8 and 9 show the relationship between the core thickness D and an increase in temperature during the transitional period, that is, between ON and OFF of the refrigerant compressor. FIG. 8 shows the evaluation result in a refrigerant cycle apparatus in which a fin thermister is attached to the outer fin 26 and the operation (i.e., on and off) of the compressor is switched based on a temperature of a core outer surface detected by the fin thermister. FIG. 9 shows the evaluation result in a refrigerant cycle apparatus in which an air thermister (i.e., evaporator downstream thermister) is disposed at a position downstream of the evaporator with respect to the air flow and the operation of the compressor is switched based on a temperature of the air detected by the air thermister.

In FIGS. 8 and 9, lines E1 and E2 show the results of the evaporator 1 of the present embodiment, and lines C1, C2 show the results of an evaporator as a comparative example. Also, the lines E1 and C1 show the result of an intermediate load condition of the refrigerant cycle apparatus, and the lines E2 and C2 show the result of a high load condition of the refrigerant cycle apparatus, in which a load is higher than that in the intermediate load condition.

As shown in FIG. 8, in a vehicular air conditioner having the fin thermister-type refrigerant cycle apparatus in which the evaporator 1 of the present embodiment is employed, the increase in temperature satisfies a first target level TL1 when the core thickness D is equal to or greater than 12 mm. Also, the increase in temperature satisfies a second target level TL2 when the core thickness D is equal to or greater than 20 mm. Further, the increase in temperature satisfies a third target level TL3 when the core thickness D is equal to or greater than 37 mm. Here, the first target level TL1 is, for example, a level that is required in the latest vehicle model. The second target level TL2 is a level in which a person hardly feels a variation in temperature in a sensory evaluation. The third target level TL3 is a level in which a person does not feel the variation in temperature in the sensory evaluation.

As shown in FIG. 10, the second target level TL2 corresponds to a case where a variation in temperature of air at an air outlet in a passenger compartment is equal to or less than 5 degrees Celsius. In this case, a variation in temperature of air discharged from the evaporator needs to be equal to or less than 7 degrees Celsius. The third target level TL3 corresponds to a case where the variation in temperature of air at the air outlet in the passenger compartment is equal to or less than 3 degrees Celsius. In this case, a variation in temperature of air discharged from the evaporator needs to be equal to or less than 5 degrees Celsius.

That is, in the fin thermister-type apparatus, the evaporator 1 having the core thickness D in the range between 12 mm and 50 mm satisfies the first target level TL1 at least. The evaporator 1 having the core thickness D in the range between 20 mm and 50 mm reduces the variation in temperature to a level where a person hardly feels the change of temperature of air blown from the air outlet. Further, the evaporator 1 having the core thickness D in the range between 37 mm and 50 mm reduces the variation in temperature to a level where a person does not feel the change of temperature of air blown from the air outlet.

On the other hand, with regard to the evaporator of the comparative example, the core thickness D needs to be greater than approximately 53 mm so as to satisfy the first target level TL1 at least.

As shown in FIG. 9, in an air conditioner having the air thermister-type refrigerant cycle apparatus in which the evaporator 1 of the present embodiment is employed, the increase in temperature satisfies the first target level TL1, which exemplarily corresponds to a level required in a next vehicle model, when the core thickness D is equal to or greater than 22 mm. The increase in temperature satisfies the second target level TL2 when the core thickness D is equal to or greater than 31 mm. The increase in temperature satisfies the third target level TL3 when the core thickness D is equal to or greater than 48 mm.

On the other hand, with regard to the evaporator of the comparative example, the core thickness D needs to be increased greater than approximately 58 mm so as to satisfy the first target level TL1 at least.

That is, in the air thermister-type apparatus, the evaporator 1 having the core thickness D in the range between 22 mm and 50 mm satisfies the first target level TL1 at least. The evaporator 1 having the core thickness D in the range between 31 mm and 50 mm reduces the variation in temperature to a level where a person hardly feels the change of temperature of air blown from the air outlet. Further, the evaporator 1 having the core thickness D in the range between 48 mm and 50 mm reduces the variation in temperature to a level where a person does not feel the change of temperature of air blown from the air outlet.

In the evaporator 1 of the present embodiment, in a case where a total cross-sectional area (passage area) of the third path 213 of the first tube row 21 is set smaller than a total cross-sectional area (passage area) of the first lower tank 41, the stagnation of the liquid refrigerant is further reduced.

On the other hand, in a case where the total cross-sectional area (passage area) of the third path 213 of the first tube row 21 is set greater than the total cross-sectional area (passage area) of the first lower tank 41, the performance of the heat exchange is improved.

Other Embodiments

In the above embodiment, the refrigerant inlet 51 is in communication with the end of the first lower tank 41 through the side passage 210, and the refrigerant outlet 52 is in communication with the end of the second upper tank 32. The refrigerant inlet 51 and the refrigerant outlet 52 are located on the same end of the evaporator 1 with respect to the core width direction. However, the arrangement of the refrigerant inlet 51 and the refrigerant outlet 52 is not limited to the above arrangement.

The refrigerant inlet 51 can be provided to be in communication with the first header tank 11, and the refrigerant outlet 52 can be provided to be in communication with the second header tank 12 as long as the refrigerant inlet 51 and the refrigerant outlet 52 are located on the same end of the evaporator 1 with respect to the core width direction.

For example, as shown in FIG. 11, the refrigerant inlet 51 can be provided to be directly in communication with the first lower tank 41 of the first header tank 11, and the refrigerant outlet 52 can be provided to be directly in communication with the second upper tank 32 of the second header tank 12. Also in this case, the refrigerant inlet 51 and the refrigerant outlet 52 are provided on the same end of the evaporator 1 with respect to the core width direction.

In the above embodiment, the third path 213 of the first tube row 21 and the first path 221 of the second tube row 22 are configured to provide the parallel upward currents. However, the flow pattern of the refrigerant in the third path 213 and the first path 221 is not limited to the above pattern as long as the first furthest path of the first tube row 21 provides the refrigerant upward current. Also, the number of paths in each of the first and second tube rows 21, 22 is not limited to three.

In the above embodiment, the core 2 has two rows of the tubes 20 with respect to the air flow direction. However, the number of rows of the tubes 20 is not limited to two rows. For example, the core 2 can have three or more rows of the tubes 20.

The present invention is effectively employed to the refrigerant evaporator having the core in which the first tube row 21 is located on a downstream-most side of the core 2, the second tube row 22 is located on an upstream-most side of the core 2, and the first tube row 21 and the second tube row 22 are overlapped with each other with respect to the air flow direction.

The first communication portion and the second communication portion can be constructed of any structures, other than the first communication holes 36 and the second communication holes 46, respectively.

For example, as shown in FIG. 12, the first communication portion can be constructed of the first communication holes 36, and the second communication portion can be constructed of a second communication member 462, such as a pipe, defining a second communication passage 362 therein, in place of the second communication holes 46.

As another example, as shown in FIG. 13, the first communication portion can be constructed of a first communication member 461, such as a pipe, defining a first communication passage 361 therein, in place of the first communication holes 36. Also in this case, the second communication portion can be constructed of the second communication member 462, similar to the example shown in FIG. 12. Alternatively, the second communication portion can be constructed of the second communication holes 46, similar to the embodiment shown in FIG. 3.

In the above embodiment, the outer fins 26 are provided between the tubes 20 and are joined to the adjacent tubes 20. However, the structure of the core 2 is not limited to the above structure.

For example, the core 2 can be a finless core without having the outer fins 26 between the tubes 20. As another example, the core 2 can be a finless core that have projections between the tubes 20, in place of the outer fins 26, and the projections are, for example, made of cutting and moving portions of the tubes 20. As further another example, the core 2 can be constructed of the tubes 20 and outer fins, each of which is in contact with the tube 20 on one side. In these cores 2, because condensation generated on outer surfaces of the core 2 is effectively discharged, the temperature of the core 2 is properly detected. As such, effective response is provided.

The refrigerant is not limited to the R134a, but may be any other substances. In a case where the refrigerant is other than the R134a, the evaporator 1 provides the similar effects as described above. In the case where the refrigerant is the R134a, the above described effects are effectively provided.

In the above embodiment, the evaporator 1 is exemplarily employed to the refrigerant cycle of the vehicular air conditioner. However, the evaporator 1 can be employed to a refrigerant cycle apparatus for any other purposes.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader term is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. 

1. A refrigerant evaporator for performing heat exchange between a refrigerant and an external fluid, the refrigerant evaporator comprising: a core including a plurality of tubes, the tubes arranged in a core width direction and at least in two rows including a first row and a second row, the first row being located downstream of the second row with respect to a flow direction of the external fluid; a first header tank including a first upper tank portion and a first lower tank portion, the first upper tank portion being in communication with upper ends of the tubes of the first row, the first lower tank portion being in communication with lower ends of the tubes of the first row; a second header tank including a second upper tank portion and a second lower tank portion, the second upper tank portion being in communication with upper ends of the tubes of the second row, the second lower tank portion being in communication with lower ends of the tubes of the second row; a refrigerant inlet disposed at an end of the first header tank; a refrigerant outlet disposed at an end of the second header tank, the end of the second header tank and the end of the first header tank being on a same side with respect to the core width direction; a first separation member disposed in the first header tank such that a first upward path through which the refrigerant flows in an upward direction and a first downward path through which the refrigerant flows in a downward direction are provided by the tubes of the first row, the first upward path and the first downward path being adjacent to each other with respect to the core width direction; and a second separation member disposed in the second header tank such that a second upward path through which the refrigerant flows in the upward direction and a second downward path through which the refrigerant flows in the downward direction are provided by the tubes of the second row, the second upward path and the second downward path being adjacent to each other with respect to the core width direction, wherein a thickness of the core with respect to the flow direction of the external fluid is equal to or less than 50 mm, a width of the core with respect to the core width direction is equal to or greater than 220 mm, the first upward path is located further than the first downward path with respect to the refrigerant inlet, and a width of the first upward path with respect to the core width direction is equal to or less than 95 mm.
 2. The refrigerant evaporator according to claim 1, wherein the second upward path is located further than the second downward path with respect to the refrigerant outlet, the first upper tank portion includes a first upper chamber that is in communication with the first upward path, the first lower tank portion includes a first lower chamber that is in communication with the first upward path, the second upper tank portion includes a second upper chamber that is in communication with the second upward path, and the second lower tank portion includes a second lower chamber that is in communication with the second upward path, the refrigerant evaporator further comprising: a first communication portion configured to allow communication between the first upper chamber and the second upper chamber; and a second communication portion configured to allow communication between the first lower chamber and the second lower chamber.
 3. The refrigerant evaporator according to claim 2, wherein the tubes are arranged only in the first row and the second row, the width of the core is at least 220 mm and at most 350 mm, and the width of the first upward path is at least 50 mm and at most 95 mm.
 4. The refrigerant evaporator according to claim 3, wherein the first communication portion is provided by a first communication member defining a first communication passage therein, and the second communication portion is provided by a second communication member defining a second communication passage therein.
 5. The refrigerant evaporator according to claim 3, wherein the first upper tank portion and the second upper tank portion are disposed adjacent to each other with respect to the flow direction of the external fluid, the first lower tank portion and the second lower tank portion are disposed adjacent to each other with respect to the flow direction of the external fluid, the first communication portion defines a first communication opening between the first upper tank portion and the second upper tank portion, and the second communication portion defines a second communication opening between the first lower tank portion and the second lower tank portion.
 6. The refrigerant evaporator according to claim 5, wherein each of the first communication opening and the second communication opening has an equivalent diameter that is at least 0.55 mm and at most 3 mm.
 7. The refrigerant evaporator according to claim 3, wherein the first communication portion provides a passage area greater than that of the second communication portion.
 8. The refrigerant evaporator according to claim 3, wherein the first communication portion provides a passage area smaller than that of the second communication portion.
 9. The refrigerant evaporator according to claim 3, wherein the second upward path has a width that is equal to or greater than the width of the first upward path with respect to the core width direction.
 10. The refrigerant evaporator according to claim 3, wherein the second upward path has a width that is equal to or less than the width of the first upward path with respect to the core width direction.
 11. The refrigerant evaporator according to claim 3, wherein the second separation member is disposed in the second header tank such that the tubes of the second row provide the second upward path, the second downward path and a third upward path through which the refrigerant flows in the upstream direction, and the third upward path is located adjacent to the refrigerant outlet, the second upward path is located furthest from the refrigerant outlet and the second downward path is located between the second upward path and the third upward path.
 12. The refrigerant evaporator according to claim 11, wherein when the width of the first upward path is defined as L1, a width of the second upward path with respect to the core width direction is defined as L2, and the width of the core is defined as W, a sum of the width of the first upward path and the width of the second upward path satisfy a relationship of 0.24×W≦L1+L2≦0.36×W.
 13. The refrigerant evaporator according to claim 11, wherein the core further includes outer fins between the adjacent tubes, a dimension of each fin with respect to the core width direction is at least 3 mm and at most 7 mm, and a dimension of each tube with respect to the core width direction is at least 1.1 mm and at most 2.3 mm.
 14. The refrigerant evaporator according to claim 1 for being employed in a refrigerant cycle apparatus having a compressor whose operation is controlled based on a temperature of an outer surface of the core, wherein the thickness of the core is at least 12 mm and at most 50 mm.
 15. The refrigerant evaporator according to claim 1 for being employed in a refrigerant cycle apparatus having a compressor whose operation is controlled based on a temperature of an outer surface of the core, wherein the thickness of the core is at least 20 mm and at most 50 mm.
 16. The refrigerant evaporator according to claim 1 for being employed in a refrigerant cycle apparatus having a compressor whose operation is controlled based on a temperature of an outer surface of the core, wherein the thickness of the core is at least 37 mm and at most 50 mm.
 17. The refrigerant evaporator according to claim 1 for being employed in a refrigerant cycle apparatus having a compressor whose operation is controlled based on a temperature of air downstream of the core, wherein the thickness of the core is at least 22 mm and at most 50 mm.
 18. The refrigerant evaporator according to claim 1 for being employed in a refrigerant cycle apparatus having a compressor whose operation is controlled based on a temperature of air downstream of the core, wherein the thickness of the core is at least 31 mm and at most 50 mm.
 19. The refrigerant evaporator according to claim 1, wherein a total passage area of the first upward path is smaller than a passage area of the first lower tank portion.
 20. The refrigerant evaporator according to claim 1, wherein a total passage area of the first upward path is greater than a passage area of the first lower tank portion.
 21. The refrigerant evaporator according to claim 1, wherein the core is a finless-type without having outer fins between the tubes.
 22. The refrigerant evaporator according to claim 1, wherein the core includes fins between the adjacent tubes, and each of the fins is in contact with one of the adjacent tubes. 